1. Field of the Invention
This invention is in the field of treating mixtures of mineral solids of different sizes and moisture contents to produce a homogeneous mixture suitable for further processing, for example, in a calcining furnace.
2. Description of the Prior Art
The calcining of cement clinkers may occasionally require starting materials of very different characteristics. For example, one of the starting materials may be a clarifying sludge which results as a waste product from limestone processing. This material must be processed jointly with other components required for cement production such as limestone, sand and possibly iron into a pulverized raw material suitable for calcining in the furnace.
One method which has been used involves dehydrating the clarifying sludge by means, for example, of a pressure filter press to achieve a moisture content of approximately 20 to 22% in the filter cake. Since this sludge had a grain size which is substantially appropriate for further processing, it required only an additional drying operation and admixture with the remaining starting materials to be useful in calcining. The clarifying sludge amounted to up to 50% by weight of the pulverized raw material composition, expressed on a dry basis. The remaining 50% consisted essentially of limestone which occurred in large pieces and had a moisture content of about 6 to 8% as a result of a grinding and drying operation. In the prior art practice, the main starting materials, the clarifying sludge and the limestone were treated separately before their combination. In the case of the limestone, this meant a multi-step drying process and a separate drying process designed specifically for the clarifying sludge.